1. Field of the Invention
The present invention generally relates to a method and apparatus for circuit board inspection. In particular, the present invention relates to a method and apparatus for circuit board inspection capable of effectively monitoring inspection signals by using a signal monitor incorporated in the apparatus during inspection operations.
2. Discussion of the Background
Background inspection apparatuses for inspecting circuit boards compare reference data of a nondefective circuit board and a test circuit board to verify the functional accuracy of the test circuit board.
A background inspection apparatus stores measured data values of a nondefective circuit board as reference data values in a memory of the background inspection apparatus. When a test circuit board is inspected, its data values are measured and compared with the reference data values to verify the functional accuracy of the test circuit board.
In this application, statuses of signals from the nondefective circuit board may need to be monitored to determine more accurately whether the measured data values of the nondefective circuit board are correct. However, the background inspection apparatus does not have a function to monitor conditions of the signals.
Another background inspection apparatus uses a detection unit to detect a difference in a digital form between reference response pattern data obtained from a nondefective circuit board and response pattern data obtained from a test circuit board, and obtains results of comparison of these circuit boards.
Statuses of signals from the nondefective circuit board may also be needed to be monitored to determine more accurately whether the reference response pattern data of the nondefective circuit board is correct. However, the background inspection apparatus does not have a function to monitor conditions of the signals in common with the previously described background inspection apparatus.
To monitor the signals for searching defects of the above-described circuit boards and checking conditions of signals thereof, an external detection device, such as an oscilloscope and a logic analyzer, has been used. Based on signals of the circuit boards of a target product acquired with the external detection device by using probes, waveforms, logical values and times are studied to specify a position of a defect and to examine the conditions of signals. When the probes of the external detection device make contact with the test circuit board, a load of the probes' capacitor may deform the waveforms. The deformed waveforms may be different from the waveforms actually obtained in an adequate environment in which the actual external detection device is used to examine the conditions of the signals of the circuit boards. Therefore, the background inspection apparatus may have difficulty in verifying functional accuracy of the test circuit boards.